2. Add Two Numbers

문제

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

풀이

작은 문제(한자리 덧셈)를 해결할 수 있도록 함수를 작성한 후, 연결 리스트를 순회하면서 계산하도록 한다.

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:

        if l1 == None and l2 == None :
            return None

        if l1 == None :
            l1 = ListNode(0)

        if l2 == None :
            l2 = ListNode(0)

        val = (l1.val + l2.val) % 10
        head = ListNode(val)

        if l1.val + l2.val >= 10 :
            if l1.next == None :
                l1.next = ListNode(1)
            else :
                l1.next.val += 1

        head.next = self.addTwoNumbers(l1.next, l2.next)

        return head